The proposed transition to hydrogen is aimed at resolving global issues, such as petroleum scarcity and CO 2 emissions, so it is sensible to look at this transition at a global level. In this paper, we present a model, named the World Hydrogen Transition Model (WHTM), that seeks to achieve two goals: 1) a projection of requirements for worldwide automobile travel measured in vehicle-kilometers traveled through the end of the 21st century, and 2) a prediction of hydrogen and underlying energy resource requirements based on different scenarios for improvement in vehicle efficiency, introduction of fuel cell vehicles, and introduction of hydrogen produced from non-fossil resources. The model includes industrializing and less developed as well as industrialized countries. Results from the model suggest that, for a range of likely scenarios, energy consumption for automobile travel will be as great or greater than current levels. However, if the transition to hydrogen fuel cell vehicles can be carried out successfully in the middle of the century, and is then followed by a transition to hydrogen from non-fossil resources, total petroleum consumption and CO 2 emissions from the automobile sector could be greatly reduced compared to current levels, thereby making motorized personal transportation more sustainable. Applicability to other emerging zero-carbon vehicle options, such as plug-in hybrid electric vehicles (PHEVs), is also discussed.